T helper cells are of paramount importance in the generation of most antibody responses. The development of a new system which permits unprimed T cells to be stimulated and mature into fully effective helper cells in vitro has provided the approach necessary to study the mechanism of stimulation of T helper cells. The cell interactions involved as well as the discriminating features which dictate whether T cell help, T cell tolerance, or T cell suppression are obtained is under studies. The use of the culture system will also provide insight into the nature of T cell receptors on helper cell precursors, and on the nature of T cell effector functions - help and suppression by enabling the preparation of highly purified cell population whose metabolic activities and the molecules which are released can be studied.